1. Field of the Invention
The present invention relates to the use of aluminum tris(-ethyl phosphonate) to inhibit the nitrification of ammonium nitrogen present in the soil. Furthermore, the present invention relates to nitrogenous fertilizer compositions which contain this compound.
2. Description of the Prior Art
The use of nitrogenous fertilizers (e.g., liquid ammonia, urea, ammonium salts such as ammonium sulfate, ammonium nitrate and ammonium phosphate, and the like) to improve plant nutrition and growth is well known. These nitrogenous fertilizers, upon addition to the soil, form ammonium ions, which act as a suitable nitrogen source for cultivated crops. Specifically, because these ammonium ions are generally absorbed and retained by clay and decomposing vegetation in the soil, they remain readily available for plant utilization.
However, through the bacterial process of nitrification, ammonium ions are converted to nitrates. Although nitrates are beneficial in some situations, they have, as anions not bound to soil colloids, the undesirable characteristic of being washed or leached away easily by rain or irrigation. Thus, situations where relatively rapid nitrification of the ammonium ions is accompanied by rain or irrigation may cause a great waste of fertilizer.
To be more specific, nitrification is the process whereby ammonium-nitrogen is converted to nitrite-nitrogen and then nitrate-nitrogen. This oxidation is carried out by various microorganisms called nitrifiers as illustrated by the following sequence: ##STR1## The addition of chemical agents to the soil in order to inhibit or suppress the nitrification process and, thus, retain the nitrogen in the cationic ammonium form in the soil is well known. Such chemical agents are generally called nitrification inhibitors. These chemicals are toxic to the microorganism nitrifiers and will slow down or completely block the oxidation of ammonium ions to nitrates in the soil. More specifically, it is known that there are three types of nitrification inhibitors, namely, ammonium nitrification inhibitors; nitrite nitrification inhibitors; and ammonium-nitrite nitrification inhibitors. Ammonium nitrification inhibitors have been found to be the most commercially important of the three types because they have a positive effect, as compared to the other two types, on the nitrogen balance of soils and of many plants. See Sommer, K., Nitrificides, Landwirt. Forsch. Sonderh., Volume 27, pages 64-82 (1972) for a more detailed discussion of these three types of inhibitors.
Separately, aluminum tris(-O-ethyl phosphonate) has been disclosed as a fungicide. See Farm Chemicals Handbook, 1980, Meister Publishing Co., page D12 (1980). However, this compound has never been disclosed until the present-invention as being an ammonium nitrification inhibitor.